Synthesis, Structures And Properties Of Metal Selenite And Iodate

Since the discovery of microporous aluminophosphates AlPO₄-n in 1982, crystal engineering of organically templated open-framework materials has provoked significant interest in their new structure architectures and potential applications in the fields of photochemistry, electromagnetism, catalysis, and sorption. An astonishing variety of inorganic frameworks templated by organic species in the systems of M/O, M/Si/O, M/P/O, M/As/O, M/S/O, M/Se/O, M/Te/O (M = metal) were reported. The anionic in those systems has developed from tetrahedral coordination group (such as silicate, phosphate and sulphate) to pseudo tetrahedral coordination group (such as phosphite and selenite). In order to extend the field of the system, one could search other tetrahedral or pseudo tetrahedral coordination groups, and might focus on iodate. Iodate anion, with nonbonded electron pairs, has a pyramidal geometry, which facilitates the formation of crystallographic noncentrosymmetric (NCS) structures when iodate anions are incorporated into crystalline materials. The materials with NCS structure are of great interest due to their potential nonlinear optical, piezoelectric, pyroelectric, and ferroelectric properties. Materials containing units in asymmetric coordination environments are of current interest owing to their technologically important properties such as second-harmonic generation (SHG), piezoelectricity, ferroelectricity, and pyroelectricity. In addition to having asymmetrically coordinated units, materials exhibiting these properties must also be crystallographically noncentrosymmetric (NCS). In a seminal paper by Kurtz and co-workers it was established that the successful preparation of NCS materials was often dependent on the combination of three key structural features. First, anions with a nonbonding, but stereochemically active, pair of electrons such as selenite or iodate have a tendency to align in the solid state to create polar structures. Second, transition metals have already been recognized as being susceptible to distortion from idealized octahedral symmetry. These distortions can be cooperative and lead to noncentrosymmetric (NCS) structures. Finally, large cations such as K+, Cs+, and Rb+ have a propensity for residing in sites where they form contacts with eight or more anions in an acentric environment. While there is no guarantee that the combination of these features will yield NCS structures, the tendency for this to be true is certainly apparent from extensive reviews of this area. Considering these properties, one would expect iodate pyramidal to be able to play a role similar to that of selenite pyramidal that constructs the inorganic framework and brings some new properties to the open-framework materials.In the system of selenite, we obtained four compounds constructed by [SeO3]2-, {[VO(OH)(H₂O)](SeO3)}4·2H₂O(1) , Cu(H₂O)2SeO3(2) and M(4,4,-bipy)[(VO2)(SeO3)]2 M=Co(3),Ni(4). Compound 1 is one-dimensional chains built up from [VO6] and [SeO3]. Compound 2 is three-dimensional framework constructed from [CuO5] and [SeO3]. Componds 3 and 4 possess similar three-dimensional framework consisting of [(VO2)(SeO3)]∞helical chains and [M(4,4'-bpy)]22+ coordination complex.In the system of transition metal iodates, we obtained compounds Cu3(OH)2(IO₃)6(5), Cu(IO₃)2(6) and KMoO2(IO₃)4(7). Compound 5 is one-dimensional ribbons built of [IO₃] and [CuO4]. Compounds 6 is two-dimensional layers constructed by [CuO6] and [IO₃]. Compound 7 is one dimensional chains consisting of [MoO6] and [IO₃].Using hydrothermal synthesis, we successfully obtained three rare earth metal iodates Ln(IO₃)3 Ln=Ce(8),Pr(9),Gd(IO₃)3(H₂O)·H₂O(10) and one actinouranium iodate (UO2)(IO₃)2(H₂O)(11). Compunds 8 and 9 possess three-dimensional framework consisting of [LnO9] and [IO₃]. Compound 10 also possesses three-dimensional framework built up from [GdO8] and [IO₃]. Compound 11 present two-dimensional layer structure consisting of helical chains, which built up from [UO7] and [IO₃].In the system of I2O5-Metal (In,Mo)-Organic Ligands -H₂O, we obtained two organic templated metal iodates (H2en)KIn(IO₃)6.2(H3O)(12) and (C3H4N2)4(C4H4N2)(MoO2)6(IO6)(13). Structure determination indicates that compound 12 is zero-dimensional units consisting of [In(IO₃)6]3- anions and separated by potassium, water and ethylenediamine cations. Strikingly, the title compound possesses helical hydrogen bonds formed by organic amine templates, water molecules and inorganic network. Compound 13 is zero-dimensional cluster consisting of (MoO2)3(IO₃).